Apparatus, system, and method for managing reverse link communication resources in a distributed communication system

ABSTRACT

An apparatus, system, and method efficiently manage reverse link communication in a communication system having geographically distributed base stations. Coupled load information is exchanged between base stations allowing a base station to determine an appropriate allocation of reverse link channel resources to mobile stations served by the base station. Since the allocation of reverse link channels resources are controlled directly by the base station, delays due to communications with a central controller are eliminated. As a result, adverse effects of load scheduling based on obsolete reverse channel information are minimized.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority of U.S. Provisionalapplication Ser. No. 60/479,252, filed on Jun. 16, 2003, entitled“Method And Apparatus for Distributed Control Of Reverse LinkCommunication Load Scheduling”, and U.S. provisional application Ser.No. 60/480,155, filed on Jun. 19, 2003, entitled “Method And Apparatusfor Distributed Control Of Reverse Link Communication Load Scheduling”which are incorporated by reference in their entirety herein. Thisapplication is related to U.S. patent application Ser. No. 10/864,652filed concurrently with this application and entitled “Apparatus,System, And Method for Autonomously Managing Reverse Link CommunicationResources in a Distributed Communication System.”

BACKGROUND OF THE INVENTION

The invention relates in general to communication systems and morespecifically to an apparatus, system, and method for managing reverselink (uplink) communications in a communication system.

Many wireless communication systems employ geographically distributedbase stations to provide communication cells or regions where a servingbase station provides communication service to mobile stations withinthe region corresponding to the serving base station. In certainsituations, the reverse link signals transmitted from each mobilestation to a base station interfere with other reverse link signalstransmitted from other mobile stations. Because of the interference andlimited resources, the capacity of each base station is limited. Areverse link capacity of a base station is affected by the reverse linkload due to the mobile stations served by the base station, by thecoupled reverse link load due to mobile stations served by other basestations and by other noise sources. Reverse link load schedulingprovides a mechanism for maximizing efficient use of system resources bycontrolling the transmissions of mobile stations. In conventionalcommunication systems, a centralized controller evaluates the reverselink load and the reverse link coupled load, as well as other factors,to determine the appropriate load scheduling. For most dataapplications, however, mobile stations are controlled by a singleserving base station to reduce scheduling delays although the reverselink transmissions can affect the load at other base stations.

Conventional systems, however, are limited in several ways. For example,the communications with the centralized controller result in significantdelays. Information gathered by each base station is forwarded to thecentralized controller. The centralized controller processes theinformation, determines an optimum load capacity for each base station,and sends the optimum load capacity to each of the base stations. Eachbase station limits the communications of the mobile stations that it isserving in accordance with the updated load capacity provided by thecontroller. The channel conditions, however, often change during thetime that is required to transmit, process, and receive the optimum loadcapacity. Accordingly, a base station may be operating at a levelsignificantly different from the optimum level resulting in unusedresources or an overload condition. An overload condition may occur, forexample, where a base station operating in accordance with the latestoptimum capacity information that was provided by the controller mayoverload another base station that is attempting to operate near itsmaximum capacity because delays in the system have not allowed the newchannel conditions to be reflected in the information conveyed to thebase stations. Overload conditions lead to lost data, re-transmissionsof messages, and other undesired consequences.

Accordingly, there is need for an apparatus, system, and method forefficiently allocating reverse channel resources in a communicationsystem with geographically distributed base stations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of communication system having geographicallydistributed base stations in accordance with the exemplary embodimentsof the invention.

FIG. 2 is a block diagram of a portion of the communication system wherea single mobile station is in communication with base stationsfunctioning as a serving base station and a non-serving base station.

FIG. 3 is a block diagram of a base station in accordance with anexemplary embodiment of the invention.

FIG. 4 is a block diagram illustrating an exemplary relationship betweenthe mobile stations and the base stations in accordance with theexemplary embodiments of the invention.

FIG. 5 is a table illustrating the exemplary relationship between themobile stations and the base stations in accordance with the exemplaryembodiments of the invention.

FIG. 6 is a graphical illustration of an exemplary distribution ofreverse link loads and reverse link coupled loads experienced at a basestation in accordance with the exemplary embodiments of the invention.

FIG. 7 is a block diagram of a portion of the communication system inaccordance with the first exemplary embodiment of the invention.

FIG. 8 is a flow chart of a method of determining an expected coupledload performed at a serving base station in accordance with the firstexemplary of the invention.

FIG. 9 is a flow chart of a method of determining an available capacityat a non-serving base station in accordance with the first exemplaryembodiment of the invention.

FIG. 10 is a flow chart of managing reverse link channel resources inthe communication system in accordance with the first exemplaryembodiment of the invention.

FIG. 11 is a block diagram of a portion of the communication system inaccordance with a second exemplary embodiment of the invention.

FIG. 12 is a flow chart of a method of managing reverse link channelsperformed in a base station functioning as a serving base in accordancewith the second exemplary embodiment of the invention.

FIG. 13 is a flow chart of a method of managing reverse link channelresources at a base station functioning as a non-serving base station inaccordance with the second exemplary embodiment of the invention.

FIG. 14 is a flow chart of a method of allocating reverse link channelresources in a communication system having geographically distributedbase stations in accordance with the second exemplary embodiment of theinvention.

FIG. 15 is a block diagram of a portion of a communication systemproviding communications services to mobile stations with geographicallydistributed base stations in accordance with the third exemplaryembodiment of the invention.

FIG. 16 is a flow chart of a method, performed in a base station, ofmanaging reverse link resources in a communication system havinggeographically distributed base stations in accordance with the thirdexemplary embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An apparatus, system, and method manage reverse link communication in adistributed base station communication system. In the exemplaryembodiments discussed herein, reverse link communication isdistributively managed by base stations within a communication system.Delays associated with conventional techniques for managing reverse linkchannels are avoided since the reverse link management is not dependenton communications with a central controller. In a first exemplaryembodiment, a non-serving base station determines a coupled loadindicator based on coupled load parameters detected at the non-servingbase station due to a mobile station that has identified another basestation as the serving base station. The coupled load parameters areparameters that provide an indication of the coupled load experienced atthe non-serving base station and may include parameters such as anormalized and averaged received signal-to noise ratio (SNR) and amobile station speed. A coupled load indicator based on the coupled loadparameters is forwarded to the serving base station. The serving basestation calculates an expected coupled load at the non-serving basestation based on the coupled load indicator and a mobile stationtransmission parameter such as a scheduled transmission data rate. Theexpected coupled load is forwarded to the non-serving base station,where the non-serving base station calculates the available capacity byaccounting for the expected coupled load. Mobile stations served by thenon-serving base station are load scheduled in accordance with thecalculated available capacity.

In a second exemplary embodiment, a non-serving base station calculatesthe maximum tolerable coupled load due to the mobile stations that arescheduled by some other serving base station. The non-serving basestation determines a coupled load indicator based on coupled loadparameters (such as a normalized and averaged receive signal-to noiseratio (SNR)) at the non-serving base station due to every mobile stationthat has identified some other base station as the serving base station.In the second exemplary embodiment, the maximum tolerable coupled loadassociated with the non-serving base station is forwarded to the servingbase station every scheduling period and the measured coupled loadindicators of mobile stations are forwarded to the serving base stationat a relatively lower frequency. Since the serving base station underconsideration may also be a non-serving base station for some othermobile stations, the serving base station also determines a maximumtolerable coupled load from the mobile stations that are served by otherbase stations. The base station performs load scheduling in accordancewith the maximum tolerable coupled load reserved for mobile stations notbeing scheduled by the base station while meeting the constraintsimposed by the maximum tolerable coupled load received from other basestations.

In a third exemplary embodiment of the invention, a serving base stationschedules the mobile station reverse link transmissions in accordancewith an estimated expected coupled load due to reverse linktransmissions of mobile stations served by other base stations. Eachbase station estimates the expected coupled load due to mobile stationsserved by other base stations. Based on the estimated coupled load andthe capacity of the base station, the base station load schedules themobile stations served by the base station. In the third exemplaryembodiment, therefore, the base stations do not receive explicit ordirect coupled load information from other base stations. Accordingly,the third exemplary embodiment is particularly useful where the backhauldoes not support communication of coupled load information between basestations. Although any of several techniques may be used to calculatethe estimated coupled load, the estimations are based on previousreverse link transmissions of the mobile stations in the third exemplaryembodiment. Each base-station measures the coupled load from the mobilestations not being scheduled by the base station based on the actualtransmission rates and the measured SNR. The previous measurements ofcoupled load are fed to a statistical function that estimates theexpected coupled load during the next scheduled transmission. Thestatistical function relies on the correlation that may, in somecircumstances, be adaptively modified. The “blind” determination of theexpected coupled load, within a certain margin, determines the availablecapacity available for the base station to schedule mobile stationsserved by the base station.

FIG. 1 is a block diagram of a communication system 100 providingwireless communication services to mobile stations 110, 112, 114 usinggeographically distributed base stations 102, 104, 106, 108 inaccordance with the exemplary embodiments of the invention. FIG. 2 is aportion 200 of the communication system 100 where a single mobilestation 202 is in communication with base stations (102-108) functioningas a serving base station 204 and non-serving base station 206 to themobile station 202. At any particular time, a base station (102-108) mayfunction as a serving base station 204 or a non-serving base station 206to a particular mobile station (110-114) or may not perform any functiondirectly for the mobile station (110-114). In the interest of clarity,four base stations 102, 104, 106, 108 and three mobile stations 110,112, 114 are represented in FIG. 1. The communications system mayinclude any number of base stations (102-108) and mobile stations(110-114) as well as other communication equipment. In the exemplaryembodiments presented, the communication system 100 is a cellularcommunication system utilizing code division multiple access (CDMA)communication techniques to provide voice and data services. Thoseskilled in the art will readily recognize the various other types ofcommunication systems 100 suitable for use with the invention byapplying the teachings herein in accordance with known techniques.

Each base station 102, 104, 106, 108 provides wireless communicationservice to mobile stations (110, 112, 114) in a coverage region 116,118, 120, 122 or cell. The coverage regions 116-120 overlap such that amobile station 110-114 may be in communication with more than one basestation 102-108 at any one time. If a mobile station 110-114 is withinthe coverage region of a base station 102-108, the mobile station110-114 will identify the base station 102-108 as an active basestation. As discussed in further detail below, however, only one basestation (102-108) functions as a serving base station 204 to aparticular mobile station 202 (110-114) for data communications. Aserving base-station 204 is the base station responsible for schedulingthe next transmissions of a mobile station 202. FIG. 1 includesexemplary shapes surrounding each base station 102-108 representingserving regions 116, 118, 120, 122 where the base station 102-108 ismost likely to function as the serving base station 204 for the mobilestations 202 (110-114) within the serving region 116-122. Each mobilestation 110-114 maintains a set of active base stations in memory wheremembers of the set communicate through communication links that satisfythe required criteria. An example of a suitable method for selecting theactive base stations (102-108) for a mobile station 110-114, 202includes identifying a base station 102-108 as an active base station(102-108) 204, 206 when a signal transmitted from the base station102-108 is received at the mobile station 110-114 at an adequate level.In the exemplary embodiments, the active base stations (102-108) 204,206 are selected based on the received signal strengths of pilot signalstransmitted from the base stations 102-108, 204, 206. In somecircumstances, other techniques may be used to select the active basestations (102-108) 204, 206. The active base stations (102-108) 204, 206provide communication service to a mobile station 110-114, 202 where thequality of service and data rate may vary between the base stations102-108 due to various reasons.

In the exemplary embodiment, one of the active base stations (102-108)is selected as a serving base station 204 for the communication of dataother than voice information. Any of several techniques and criteria maybe used to select the serving base station 204. The serving base station204 may be selected based on characteristics of the forwardcommunication link 210 (from the base station 102-108 (204) to themobile station 110-114 (202)), the reverse communication link 212 (fromthe mobile station 110-114 (202) to the base station 102-108 (204)) oron both the reverse and forward communication links 212, 210. Thequality of the forward and reverse link channels 210, 212, for example,may be determined by measuring the carrier to interference ratio of thechannel. In the exemplary embodiment, information contained in a reverselink channel quality indicator channel is used to identify the servingbase station 204 and is identified by the R-CQICH channel. The servingbase station 204 responds to the communications from the mobile stations202 it is serving by performing various tasks such as allocating datatransmissions rates via scheduling grants and maintaining reverse-linkpilot received SNR above a threshold by sending power control commands.In addition, a serving base station 204 decodes the transmissions fromthe mobile station 202 and sends acknowledgements in case of hybrid-ARQwhile a non-serving base station may also decode a transmission and sendan ACK in case of a soft-handoff. The enclosed shapes representing thecoverage regions in FIG. 1 define exemplary geographic serving regions116-122 where mobile stations 110-114 within the region 116-122 willlikely have adequate communication with the corresponding base station102-108 to identify the particular base station 102-108 as the servingbase station 204. Other base stations (102-108), however, may perform asactive base stations (102-108) 206 to a mobile station 110-114, 202. Asillustrated in FIG. 1, therefore, a first mobile station 110 is within afirst serving region 116 provided by the first base station 102, asecond mobile station 112 is within a second serving region 118 providedby the second base station 104, a third mobile station 114 is within athird serving region 129 provided by the third base station 106, and thefourth base station 108 provides a fourth serving region 122.

FIG. 3 is a block diagram of a base station 300 in accordance with anexemplary embodiment of the invention. The exemplary base station 300 issuitable for use as any one of the base stations 102-108, 204, 206discussed with reference to FIG. 1 and FIG. 2. The base station 300 mayinclude any combination of hardware, software, and firmware thatperforms the functions to the base stations 102-108. The functions andoperations of the blocks described in FIG. 3 may be implemented in anynumber of devices, circuits, or software. Two or more of the functionalblocks may be integrated in a single device and the functions describedas performed in any single device or block may be implemented overseveral devices. For example, some receiving processes may be performedby the processor 304.

The base station includes a radio transceiver 302 configured tocommunicate with mobile stations 110-114 in accordance with theprotocols of the particular communication system 100. Radio frequencysignals are exchanged through the antenna 308 which may include sectorsin some circumstances. The radio transceiver 302 modulates, amplifies,and transmits signals through the forward link channels 212 and receivesand demodulates reverse link signals transmitted by the mobile stations110-114 through the reverse link channels 210.

The processor 304 is any processor, microprocessor, computer,microcomputer, or processor combination suitable for performing thecontrol and calculation functions of the base station 300 describedherein as well as facilitating the overall functionality of the basestation 300. Software code running on the processor 304 executes thesteps of methods for measuring and processing signals and for performingthe reverse link management functions of the exemplary embodiments.

A backhaul interface 306 provides an interface to the backhaul 208 ofthe communication system 100. The backhaul interface 306 includeshardware and software for exchanging signals through the backhaul 208.The processor 304 transmits and receives information to and fromcontrollers and other base stations 102-108 through the backhaulinterface 306.

FIG. 4 is a block diagram and FIG. 5 is table 500 illustrating anexemplary relationship between the mobile stations 110-114 and the basestations 102-108 in accordance with the exemplary embodiments of theinvention. The solid lines connecting base stations 102-108 to mobilestations 110-114 in FIG. 4 represent a connection between mobilestations 202 (one of 110-114) and their corresponding serving basestations 204 (one of 102-108) and dashed lines represent connectionsbetween mobile stations 202 (one of 110-114) and their non-servingactive base stations 206 (one of 102-108). As discussed herein, anon-serving active base station 206 (102-108) is a base station 300identified in the set of active base stations of a mobile station 202that is not a serving base station 204. In the exemplary situationillustrated in FIG. 4 and FIG. 5, each mobile station 110-114 maintainsa set of active base stations that includes the serving base station 204corresponding to the serving region 116-122 containing the mobilestation 110-114 and all other base stations (102-108) that arenon-serving active base stations (102-108). Accordingly, for theexemplary situation, all of the base stations 102-108 are maintained asactive base stations by each of the mobile stations 110-114. A mobilestation as a significant distance from a base station may not maintainthe base station in the set of active base stations and the base stationwill not be identified as a non-serving base station to the mobilestation even though the base station may receive reverse linkinterference from the mobile station. Only those mobile stations whosesignal strength is strong enough and their transmissions processed areconsidered by a base-station. Focusing briefly on a single mobilestation 110, the first base station 102 is the serving base station 204for the first mobile station 110, 202, and the second base station 104,third base station 106 and fourth base station 108 are non-serving basestations 206 for the first mobile station 110, 202. The reverse linktransmissions of each of the mobile stations 110-114, therefore, arereceived at each of the base stations 102-108 although only one of thebase stations 102-108 that is performing as the serving base station 204and the other base stations are performing as non-serving (active) basestations 206 for any particular mobile station 110-114 in this example.As a result, the reverse link loads and reverse link coupled loadsexperienced at a base station 102 are due to the reverse link loads ofthe mobile station 110 served by the base station 102 and the coupledloads resulting from transmission of other mobile stations 112, 114.

FIG. 6 is an illustration of a load pie chart 600 of an exemplarydistribution of reverse link loads and reverse link coupled loadsexperienced at a base station 102-108 in accordance with the exemplaryembodiments of the invention. The various sections 602-608 of the loadpie chart represent the combined reverse link load resulting from mobilestations 110-114 that can be measured or simulated for an exemplarysituation. At any base station 102-108, the total combined reverse linkload may result from transmissions from mobile stations 110-114 whereeach portion (602-608) of the total reverse link load is due to mobilestations (110-114) in a particular category. The load portions (602-608)may include a non-serving coupled load portion 602, a serving non-singleload portion 604, a serving single portion 606, and an unaccountedcoupled load portion 608. The non-serving coupled load portion 602includes the coupled reverse link load due to all of the mobile stations(110-114) that include the base station (102-108) within their set ofactive base stations but that are being served by base stations(102-108) other than the base station (102-108). The mobile stations110-114 contributing to the non-serving coupled load portion 602,therefore, have not identified the base station (102-108) as the servingbase station 204.

The non-single serving load portion 604 includes the combined reverselink load of all mobile stations 110-114 that are being served by thebase station (102-108) but include other base stations (102-108) intheir list of active base stations. The mobile stations 110-114contributing to the non-single serving load portion 604, therefore, haveidentified the base station (102-108) as the serving base station butalso have identified other base stations (102-108) as non-serving activebase stations.

The single serving load portion 606 includes the combined reverse linkload of all mobile stations served by the base station (102-108) wherethe base station (102,108) is the only base station in the set of activebase stations of any of the mobile stations 110-114.

The unaccounted load portion 608 includes all other reverse link signalsand noise that contribute to the total reverse link load that has notbeen included in any of the other load portions 602, 604, 606. Anexample of a source that may contribute to the unaccounted load portion608 includes the reverse link transmissions from mobile stations that donot include the base station in their active set but are sufficientlyclose to the base station to contribute to total coupled load. Suchmobile stations are too far to have an adequate communication link withthe base station to include the base station in the set of active basestation but the sum total of their insignificant contributions is largeenough to take a share in the reverse-link capacity.

The relative size of the load portions 602-608 will vary over time inmost situations because of the constantly changing channel conditions.The changing channel conditions may be due to several factors such asthe motion of the mobile stations 110-114, the motion of obstacles, orthe need to offload mobile stations 110-114 and to transfer mobilestations between base stations due to severely non-uniform distributionof mobile stations 110-114. When the combined load of all of theportions 602-608 exceeds the capacity of the base station 102-108, thequality of service (QoS) to the mobile stations suffers, the systembecomes slightly unstable and coverage of the cell decreases leading tocall drops. Where the load is less than the capacity of the base station102-108, an inefficient use of resources can occur if the data rates arenot adjusted in accordance with the requests of the mobile stations110-114. In accordance with the exemplary embodiments, the reverse linkcommunications are managed by the base stations 102-108 to efficientlyallocate reverse link resources to (load schedule) the mobile stations110-114. Reverse link resources include, for example, data rates andpower levels that contribute to a load to the base station 102-108.

FIG. 7 is a block diagram of a portion 700 of a communication system 100providing communications services to mobile stations 110-114 withgeographically distributed base stations 102-108 in accordance with thefirst exemplary embodiment of the invention. In most situations, thecommunication system 100 includes several base stations 704, 706 thatare strategically positioned to provide wireless communication servicesto numerous mobile stations 702. Depending on the quality of thecommunication channels between a mobile station 702 and the base station(704,706), the mobile station 702 may be communicating with more thanone base station (704, 706) at any particular time. As discussed above,each mobile station 702 maintains a set of active base stations wherethe communication links between the mobile station 702 and the activebase stations 704, 706 are adequate for communication. Of the activebase stations, one base station performs as the serving base station 704while the other base stations in the active set are non-serving basestations 706. Such situations typically occur during a soft handoffwhere a single base station performs the functions of a serving basestation 704 and one or more other base stations are non-serving activebase stations 706. Where conditions warrant, the role of the servingbase station 704 is transferred to a base station previously functioningas a non-serving active base station 706 (i.e. a handoff occurs).

In the interest of clarity, FIG. 7 includes blocks representing a mobilestation 702 and two active base stations 704, 706 including a servingbase station 704 and non-serving base station 706. Those skilled in theart will recognize, based on these teachings and known techniques, thata base station 300 may function as a serving base station 704 tonumerous mobile stations 702 and that any one mobile station 702 maymaintain any number of active base stations 704, 706. The teachingsdiscussed herein, therefore, may be extended to any number of mobilestations 702, serving base stations 704, and non-serving base stations706. As discussed below in further detail, the other base stations 300may not have a communication link with the mobile station 702 ofsufficient quality to become an active base station but may contributeto the load experienced at any one of the active base stations 704, 706.The serving base station 704 may be the first base station 102, thesecond base station 104, or third base station 106 discussed above withreference to FIGS. 1-4. The serving base station 704 may also functionas a non-serving base station 706 for another mobile station (not shownin FIG. 7) and the non-serving base station 706 may function as aserving base station 704 for other mobile stations (not shown in FIG.7). Accordingly, a base station 102-108 may simultaneously function as aserving base station 704 to some mobile stations 702 and as anon-serving base station to other mobile stations. The functionsdescribed herein for each of the base stations 704, 706, therefore, aresimultaneously performed by the other of the base stations in mostcircumstances.

In the first exemplary embodiment, a base station 300 functioning as thenon-serving base station 706 determines an expected available capacitybased on an expected coupled load 712 received from another base station300 functioning as the serving base station 704 where the expectedcoupled load 712 indicates an expected coupled load at the non-servingbase station 706 resulting from reverse link transmissions 210 of amobile station 702 being served by the serving base station 704. Theserving base station 704 determines the expected coupled load 712 usingthe coupled load indicator 710 received from the non-servingbase-station 706 and the parameters associated with the next scheduleddata transmission rate. If there are multiple mobile stations 702 thatare served by the serving base station 704 and that include thenon-serving base-station 706 as a non-serving base station, the expectedcoupled load 712 can be the sum of expected coupled loads determined foreach of the mobile stations based on the expected coupled load 712 andscheduled transmission data rates. The non-serving base station 706receives and processes the reverse link transmissions 210 of the mobilestation 702 to determine one or more coupled load parameters a such as anormalized and averaged receive signal-to noise ratio (SNR). An exampleof another coupled load parameter is a speed of the mobile station 702.Based on the coupled load parameters, the non-serving base station 706calculates the coupled load indicator 710. The coupled load indicator710 is forwarded to the serving base station 704. The serving basestation 704 determines an expected coupled load at the non-serving basestation 706 using the coupled load indicator 710 and a transmissionparameter of the mobile station 702. The expected coupled load is thecoupled reverse link load that will result at the non-serving basestation 706 due to an anticipated future reverse link transmission ofthe mobile station 702. The serving base station 704 forwards a valuerepresenting the expected coupled load 712 to the non-serving basestation 706. The non-serving base station 706 calculates the expectedavailable capacity at the non-serving base station 706. Using theexpected available capacity, the non-serving base station 706 managesthe reverse link transmissions of other mobile stations (not shown) thatare served by the non-serving base station 706 by appropriately loadscheduling the mobile stations it is serving. Where there is more thanone mobile station 702, the non-serving base station 706 measures andcomputes a coupled load indicator 710 for each mobile station 702 thatmaintains the non-serving base station 706 within the active set. Acoupled load indicator 710 is forwarded to each serving base station 704associated with the mobile stations 702 that identify the non-servingbase station 706 as an active base station.

In the first exemplary embodiment, the coupled load indicator 710 is anenergy-per-chip-to-noise-plus-interference ratio (Ecp/Nt), where Ecprepresents the energy per pilot signal chip. If the reverse link pilotis power controlled, an average expected (Ecp/Nt) is computed byaveraging chip (Ecp/Nt) over a particular duration. The coupled loadindicator 710 may be the average expected (Ecp/Nt) or any function ofthe average expected (Ecp/Nt).

Although other methods may be used in some circumstances to forward thecoupled load indicator 710 to the serving base station 704, the coupledload indicator 710 is transmitted through the backhaul 208 in the firstexemplary embodiment. Accordingly, appropriate messaging and addressingis used to rout the coupled load indicator 710 through the backhaul 208.The backhaul interface 306 performs any required translations, orprocessing to exchange the coupled load indicators through the backhaul.In some circumstances, the coupled load indicator 710 can be transmittedthrough a direct communication link between the non-serving base station706 and the serving base station 704. For example, a radio frequency ormicrowave point-to-point system link can be used to transmit coupledload indicator 710 in some situations. Further, in some circumstances,the coupled load indicator 710 may be conveyed through the mobilestation 702.

In the first exemplary embodiment, the serving base station 704identifies the mobile stations 702 that are expected to transmit duringthe next transmit cycle and generates the expected coupled load 712based on the coupled load indicators 710 (for example Ecp/Nt) receivedfrom the non-serving base station 706 and the transmission data ratethat the mobile station 702 has been authorized (scheduled) to useduring the next transmission. The transmission parameter, therefore, atleast includes the anticipated data rate of the mobile station 702 inthe first exemplary embodiment. In addition, other transmissionparameters may be used to calculate the expected coupled load at thenon-serving base station 706, such as secondary pilot transmissions orcontrol channels traffic-to-pilot ratio. In scenarios where theautonomous transmission on control and voice channels take place, theexpected coupled load 712 may account for the average expected coupledload contributed by these channels. In the first exemplary embodiment,the expected coupled load 712 is some function of the expected Ecp/Ntthat will be experienced by the non-serving base station 706 in theanticipated future transmission of the mobile station 702 and othertransmission parameters including the scheduled transmission data rate.The serving base station 704 generates the expected coupled load 712based on the coupled load indicator 710 and forwards the expectedcoupled load 712 to the non-serving base station 706. The expectedcoupled load 712, therefore, is based on the measured Ecp/Nt at thenon-serving base station 704, the reverse link transmission power oncontrol and voice channels, and the data rate on the traffic channel ofthe mobile station 702 in the first exemplary embodiment. The expectedcoupled load 712, however, may represent other values in somecircumstances. For example, the expected coupled load 712 my representan expected change in the coupled load that will be experienced at thenon-serving base station as compared to a previous transmission.

Where the serving base station 704 is serving more than one mobilestation 702 that has included at least one other non-serving basestation 706 within the set of active base stations, the serving basestation 704 generates an expected coupled load 712 for each non-servingbase station 706 that has forwarded a coupled load indicator 710 to theserving base station 704. Accordingly, any particular base station 300functioning as a non-serving base station 706 may receive an expectedcoupled load 712 from any number of base stations 300 functioning asserving base stations 704.

In the first exemplary embodiment, the expected coupled load 712 istransmitted through the backhaul 208 to the non-serving base station704. The backhaul interface 306 performs the required processing andformatting to transmit the expected coupled load 712 through thebackhaul 208 to the base station 300 functioning as the non-serving basestation 704. In some situations, other techniques may be used to forwardthe expected coupled load 712.

After a base station 300 has received the expected coupled load 712 fromall of the appropriate serving base stations 704 of mobile stations 702contributing to the non-serving coupled load portion 602 of the totalload, the non-serving base station 706 (300) determines the availablecapacity. The total of all of the expected coupled loads 712 is theexpected non-serving coupled load portion of the total load at the basestation 300. The available capacity is the difference of the totalcapacity of the non-serving base station 706 (300) and the total of theexpected non-serving coupled load portion (402), and the unaccountedload portion 408. After taking into account loads due to voice orfundamental reverse channel traffic, the available capacity (CAV) at abase station 300 can therefore be expressed as:C _(AV) =C _(TOT)−(Load_(Ex)+Load_(UA))where C_(TOT) is the total capacity of the cell after taking intoaccount the loads due to voice and fundamental reverse channel traffic;Load_(Ex) is the expected non-serving coupled load due to the mobilestations that are served by other base stations and for which the basestation is included in the set of active base stations; and Load_(UA) isthe load due to other sources.

Using the available capacity, the base station 300 functioning as anon-serving base station 706 for the mobile station 702 allocatesreverse link resources (load schedules) the mobiles stations (not shown)that it is serving. In the exemplary embodiment, the non-serving basestation 706 load schedules the mobile stations that do not have anyother base stations in their active base station after allocatingresources to the mobile stations maintaining other active base stations.

FIG. 8 is flow chart of a method of determining an expected coupled loadperformed at a base station 300 functioning as a serving base station704 to at least one mobile station 702 in accordance with the firstexemplary of the invention. In some circumstances, the method discussedin FIG. 8 is performed in a base station 300 that is also functioning asa non-serving base station 706. The method described with reference toFIG. 8 is performed where at least one non-serving base station 706 ismaintained in the set of active base stations of at least one mobilestation 702 that is being served by the serving base station 704. Thetechniques discussed herein can be applied to any number of basestations 300 and mobile stations 110-114. In the exemplary embodiments,the methods are performed at least partially with software code runningon the processor 304 within one or more base stations 300. Those skilledin the art will readily recognize the various techniques that can besued to implement the methods discussed based on the teachings herein inaccordance with known techniques.

At step 802, a coupled load indicator 710 is received from a basestation 300 functioning as a non-serving base station 706 to at leastone mobile station 702. The coupled load indicator 710 indicates thecoupled load measured at the non-serving base station 706 due to themobile station 702 served by another base station 300 functioning as theserving base station 704 to the mobile station 702. The non-serving basestation 706 is included within the set of active base stationsmaintained by the mobile station 702. In the first exemplary embodiment,the coupled load indicator 710 represents the ECP/NT measured at thenon-serving base station 706.

At step 804, the serving base station 704 determines an expected coupledload 712 at the non-serving base station 706 due to the mobile station702 based on the coupled load indicator 710 and at least onetransmission parameter. In the first exemplary embodiment, the servingbase station 704 calculates the expected coupled load 712 for the mobilestations 702 that are expected to transmit on the next transmissionbased on the coupled load indicator 710 measured at the non-serving basestation 706, the mobile station's scheduled data transmission rate forthe future anticipated transmission, and the transmission power level ofthe mobile station 702. The expected coupled load, therefore, is theexpected load to the non-serving base station 706 due to reverse linktransmissions of the mobile station 702 that includes at least theserving base station 704 and the non-serving base station 706 in themobile station's list of active base stations.

At step 806, the expected coupled load 712 is forwarded to the basestation 300 functioning as the non-serving base station 706 to themobile station 702. In the first exemplary embodiment, the expectedcoupled load 712 represents the expected loading as a function of thescheduled transmission data rate and the expected ECP/Nt level at thenon-serving base station 706 due to a future anticipated transmissionsof the mobile station 702. The expected coupled load 712, however, mayrepresent other parameters or values. For example, the expected coupledload 712 may represent an anticipated change in the load experienced atthe non-serving base station 706 due to the future transmission of themobile station 702 as compared to a previous transmission. In the firstexemplary embodiment, the expected coupled load indicator 712 isformatted to conform to the appropriate protocol and is transmittedthrough the backhaul 208 of the communication system 100. The expectedcoupled load indicator 712 may be forwarded to the non-serving basestation 706 using other techniques. For example, a direct linkcommunication link between the serving base station 704 and thenon-serving base station 706, such as point-to-point microwave link, canbe used to convey the expected coupled load.

FIG. 9 is a flow chart of a method of determining an available capacityat a base station 300 functioning as a non-serving base station 706 inaccordance with the first exemplary embodiment of the invention. In somecircumstances, the method discussed in FIG. 9 is performed in a basestation 300 that is also functioning as a serving base station 704 toother mobile stations 110-114. The method described with reference toFIG. 9 is performed where the set of active base stations maintained atleast at one mobile station 702 includes the non-serving base station706 and a serving base station 704. The techniques discussed herein canbe applied to any number of base stations 300 and mobile stations110-114.

At step 902, an expected coupled load 712 is received from a basestation 300 functioning as a serving base station 704 of a mobilestation 702 that maintains a set of active base stations that includesat least the non-serving base station 706 and the serving base station704. As discussed above, the expected coupled load 712 represents theexpected coupled load that will likely be experienced at the non-servingbase station 706 due to an anticipated future transmission of the mobilestation 702.

At step 904, the base station 300 functioning as the non-serving basestation 706 determines the available capacity at the non-serving basestation 706 based on the expected coupled load 712. After taking intoaccount the voice and non-scheduled reverse traffic data, thenon-serving base station 706 determines the available capacity bycalculating the difference between the total capacity and the sum of allloads and expected coupled loads. The remainder indicates the availablecapacity of the non-serving base station 706 that can be used for mobilestations 110-114 that the non-serving station 706 may be serving as aserving base station.

At step 906, the base station 300 functioning as the non-serving basestation 706 allocates reverse link channel 212 resources (loadschedules) mobile stations 110-114 served by the base station 300functioning as the non-serving base station 706 to the mobile station702 in accordance with the available capacity. The non-serving basestation 706 allocates the available capacity by limiting power levelsand data rates of any mobile stations 110-114 that are being served bythe non-serving base station 706.

In the exemplary embodiment, the methods described with reference toFIG. 8 and FIG. 9 are performed within several geographicallydistributed base stations 300 where any of the base stations 300, at anytime, may be functioning solely as a serving base station 704, solely asan non-serving base station 706, or as both a serving base station 704for one or more mobile stations 110-114 and a non-serving base station706 for one or more other mobile stations 110-114. Further, a mobilestation 702 may maintain a set of active base stations that includesseveral non-serving base stations 706 in addition to the serving basestation 704. Accordingly, in order to efficiently mange the reverse linkloads at the various base stations 300, the coupled load indicators 710and expected coupled loads 712 are conveyed to the appropriate basestations 300 and the calculations are performed taking into account thevarious parameters received from multiple base stations 300.

FIG. 10 is a flow chart of a method of allocating reverse link channelresources in a communication system 100 having geographicallydistributed base stations 300 in accordance with the first exemplaryembodiment of the invention. As discussed above, the functions ofserving base stations 704 and non-serving base stations 706 may beperformed within a single base station 300 that functions as servingbase station 704 to some mobile stations 110-114 and as a non-servingactive base station 706 to other mobile stations 114.

At step 1002, the base stations 300 functioning as serving base stations704 receive coupled load indicators 710 measured at base stations 300functioning as non-serving base stations 706 where the coupled loads aredue to the reverse link transmissions from mobile stations 702 served bythe serving base stations 704 and that maintain a set of active basestations that include the one or more of the non-serving base stations706. Each non-serving base station 706 generates a coupled loadindicator 710 that, along with the rate of transmission, represents themeasured coupled load at the non-serving base station 706 due to themobile stations that are served by another base station 300. The coupledload indicators 710 are transmitted by the non-serving base stations 706to the corresponding serving base station 704 through the backhaul 708.

A suitable notation for characterizing and describing relationshipsbetween the various base stations 300, 704, 706 includes usingsubscripts to denote a set of base stations. In the first exemplaryembodiment, each base station (BS j) that is in the active set of mobilestations (MSi), except where BS j∈ServingBS_MS_(i), measures andtransmits the (Ecp/Nt)ji to the serving base station for MSi. In thefirst exemplary embodiment, (Ecp/Nt)ji is used as a coupled loadindicator. ServingBS_MSi is the set of serving base stations for mobilestations (i) and(Ecp/Nt)ji(1+(T/P)(Ri)+(C/P))/(1+(Ecp/Nt)ji(1+(T/P)(Ri)+(C/P))) is thecoupled load experienced at the non-serving base stations (BSj) due tomobile stations (MSi) served by the serving base stations. (T/P)(Ri) isthe traffic-to-pilot ratio of the traffic channel when the transmissionrate is Ri. (C/P) is the sum total of control channels (and fundamentalchannels) power to pilot power ratios. In the exemplary embodiment, avalue representing the (Ecp/Nt)ji is transmitted to the serving basestations (BSk).

At step 1004, each serving base station 704 identifies the mobilestations 702 served by the serving base station 704 and expected totransmit during a future transmission period. For each base station(BSk), the BSk determines a set (FSk) that includes the mobile stationsthat are served by BSk and have a priority exceeding a minimum priority.

At step 1006, each serving base station 704 determines expected coupledloads 712 to the non-serving base stations 706 due to the mobilestations 702 that the serving base station 704 is serving. The servingbase station 704 determines the coupled load for each of the mobilestations 702 that are anticipated to transmit (i.e. that are members ofset FSk) based on the received coupled load indicators 710 received atthe serving base stations 704 and transmission parameters of the mobilestations 702. Accordingly, the BSk determine the expected coupled loadsfor all MSi in FSk in other BSj, where these BS j∉ServingBS_MS_(i):

${{CoupledLoad}_{kj}\text{(}R_{i}},{{\left( {E_{cp}/N_{t}} \right)_{ji}\text{)}} = {{\sum\limits_{\underset{j \in {{ActiveSet}{(i)}}}{i \in {FS}_{k}}}\frac{{Sin}\;{r_{ji}\left( {R_{i},\left( {C/P} \right)} \right)}}{1 + {{Sin}\;{r_{ji}\left( {R_{i},\left( {C/P} \right)} \right)}}}} - {\sum\limits_{\underset{j \in {{ActiveSet}{(i)}}}{i \in {FS}_{k}}}\frac{{Sin}\;{r_{ji}\left( {0,\left( {C/P} \right)} \right)}}{1 + {{Sin}\;{r_{ji}\left( {0,\left( {C/P} \right)} \right)}}}}}}$where CoupledLoad_(kj) is the total coupled load experienced at BS_(j)due to MS_(i) served by BS_(k), Sin r_(ji)(R_(i),E[R_(FCH)]) is theestimated signal to interference ratio if the MS_(i) is assigned a rateR_(i) on R-SCH and E[R_(FCH)]) is the sum total of control channels(including fundamental voice channel and secondary pilot channel) powerto pilot channel power. Sin r_(ji)(R_(i),(C/P)) is related to(Ecp/Nt)_(ji) according to the following equation:Sin r _(ji)(R _(i),(C/P))=(E _(cp) /N _(t))_(ji)(1+(T/P)(R _(i))+(C/P))where (T/P)(R_(i)) is the traffic-to-pilot power ratio when thetransmission rate on the traffic channel scheduled by serving basestation is R_(i).

At step 1008, each of the serving base stations 704 forwards theexpected coupled load (CoupledLoadkj) to the non-serving base stations706. The expected coupled loads 712 represent the expected coupled loadscalculated by the serving base stations 704. Each base station (BSk)forwards CoupledLoadkj to all other base stations. In the exemplaryembodiment, the expected coupled loads 712 are transmitted through thebackhaul 208.

At step 1110, each base station 300 functioning as a non-serving basestation 706 to at least one mobile station 702 and receiving an expectedcoupled load 712 determines an available capacity of the non-servingbase station 706 based on the expected coupled load 712. Since each ofthe non-serving base stations 706 may be a serving base station 704 forother mobile stations, each serving base station 704 receives a coupledload indicator from other serving base stations 704 if the particularserving base station 704 is also a non-serving base station 706.Accordingly, each non-serving base station 706 of BSk receiving aCoupledLoadjk determines the available capacity at the BSk using theexpression:

${CoupledinLoad}_{k} = {\underset{j \notin {{BS}{(k)}}}{\sum\limits_{j,{j \neq k}}}{CoupledLoad}_{jk}}$Cav_(k) = Cav_base_(k) − CoupledinLoad_(k)where CoupledinLoad_(k) is the sum of the coupled loads received fromthe other serving base stations 704, and Cav_(k) is the availablecapacity at the serving base station 704 after taking into account allother load contributions from voice and fundamental reverse channel datatraffic.

At step 1012, the serving base stations 704 that are also functioning asnon-serving base stations 706 allocate reverse link channel resources tothe mobile stations 110-114 (i.e. load schedules mobile stations) inaccordance with the available capacity for the serving base station 704.In the first exemplary embodiment, therefore, each serving base station704 that is also non-serving base stations 706, load schedules themobile stations MSi that are served by the serving base station 704 thatalso maintain other active base stations according to the followingequations:

${CoupledoutLoad}_{k} = {\underset{j \in {{BS}{(k)}}}{\sum\limits_{j}}{CoupledLoad}_{kj}}$Cav_(k) = Cav_(k) − CoupledoutLoad_(k)where CoupledoutLoadk is the scheduled load of all of the mobilestations with multiple base stations in the active set but served byserving base station. CoupledoutLoadkj is same as CoupledinLoadkj thatwas forwarded by BSk to the BSj. In accordance with the remainingavailable capacity after scheduling the mobile, the serving basestations BSk allocate the reverse channel resources to the mobilestations that maintain only the serving base station as the only activebase station.

Therefore, in accordance with the first exemplary embodiment of theinvention, each base station 300 that is a member of a set of activebase stations of a mobile station 702 measures and forwards the coupledloads due to those mobile stations 702 served by other base stations 704to the serving base stations 704 of the mobile station 702. Each servingbase station 704 calculates an expected coupled load 712 for thosemobile stations 702 served by the calculating base station 704 andmaintaining other active base stations. Each serving base station 704calculates an available capacity based on the expected coupled loadsreceived from other base stations 300 that are functioning as servingbase stations 704 to other mobile stations. Accordingly, each basestation 300 determines the available capacity based on the expectedcoupled loads calculated by the other base stations that are serving themobile stations that contribute to the total load at the base station300. Resources are efficiently allocated without the use of a centralcontroller thereby minimizing delays and reducing the likelihood ofretransmissions and lost data.

FIG. 11 is a block diagram of a portion 1100 of a communication system100 in accordance with the second exemplary embodiment of the invention.In the interest of clarity, FIG. 11 includes blocks representing twomobile stations 1102 and two active base stations 1104, 1106 including aserving base station 1104 and a non-serving active base station 1006.Those skilled in the art will recognize based on these teachings andknown techniques that a base station may function as a serving basestation 1104 to numerous mobile stations 1102 and that any one mobilestation 1102 may maintain any number of active base stations 1104, 1106.The teachings discussed herein, therefore, may be extended to any numberof mobile stations 1102, serving base stations 1104, and non-servingbase stations 1006. The serving base station 1104 may be the first basestation 102, the second base station 104, or third base station 106discussed above with reference to FIGS. 1-4. The serving base station1104 may also function as an active non-serving base station 1106 foranother mobile station (not shown in FIG. 11) and the non-serving basestation 1106 may function as a serving base station for other mobilestations (not shown in FIG. 11). Accordingly, a base station maysimultaneously function as a serving base station 1104 to some mobilestations and as a non-serving active base station 1106 to other mobilestations 1102. The functions described herein for each of the basestations 1104, 1106, therefore, are simultaneously performed by theother of the base stations 1104, 1106 in most circumstances.

In a second exemplary embodiment, a base station 300 functioning as anon-serving base station 1106 determines the maximum tolerable coupledload for mobile stations 1102 served by another base station functioningas the serving base station 1104. Based on the total capacity of thenon-serving base station 1106 and the load due to other mobile stations(not shown) served by the non-serving base station 1106, the non-servingbase station 1106 determines a maximum tolerable coupled load due tomobile station 1102 not served by the non-serving base station 1106. Inthe second exemplary embodiment, the non-serving base station 1106reserves capacity for the mobile stations that have some other basestation 1104 as serving base station. The non-serving base station 1106determines the maximum tolerable coupled load that the mobile stations1102 served by base station 1104 can contribute to the total load at thenon-serving base station 1106. The non-serving base station 1106 thenforwards the sum total of maximum tolerable coupled loads 1112 for allmobile stations 1102 served by the serving base station 1104 thatmaintain the non-serving base station 1106 in their set of active basestations. The non-serving base station 1106 determines a coupled loadindicator for each mobile station 1102. The coupled load indicators 1110represent the measured traffic quality estimate at the non-serving basestations due to the reverse links transmissions of the mobile stations1102. In CDMA systems with a power-controlled pilot channel, a long termaveraged and expected pilot SNR is a suitable coupled load indicator.The serving base station 1104 allocates reverse link resources to themobile stations 1102 in accordance with the maximum tolerable coupledload. In the second exemplary embodiment, the serving base station 1104allocates reverse link resources in accordance with two sets ofconstraints. The first set of constraints is imposed by the capacity ofthe serving base station 1104 and requires that the transmission datarate allocated to the mobile stations 1102 should create a load at theserving base station 1104 that is less than the available capacity atthe serving base station 1104. The second set of constraints is imposedby the maximum tolerable coupled load 1112 reported by the non-servingbase stations 1104. The rate allocated by the serving base station 1104to all the mobile stations 1102 with non-serving base station 1106 intheir active set should create a load at the non-serving base station1106 that is less than the maximum tolerable coupled load. The coupledload indicators 1110 and the allocated transmission data rate determinethe expected load contributed by the mobile station 1102 at thenon-serving base station 1104.

FIG. 12 is a flow chart of a method of managing reverse link channelsperformed in a base station 300 functioning as a serving base inaccordance with the second exemplary embodiment of the invention. Insome circumstances, the method discussed in FIG. 12 is performed in abase station 300 that is also functioning as a non-serving base station1106. The method described with reference to FIG. 12 is performed whereat least one non-serving base station 1106 is maintained in the set ofactive base stations of at least one mobile station 1102 that is beingserved by the serving base station 1104. The techniques discussed hereincan be applied to any number of base stations 300 and mobile stations1102.

At step 1202, a base station 300 functioning as the serving base station1104 receives a maximum tolerable coupled load 1112 representing amaximum tolerable coupled load at another based station 300 serving as anon-serving base station 1106 to a mobile station 1102. The maximumtolerable coupled load 1112 is determined by the non-serving basestation 1106 based on priority and service rate requests of mobilestations served by the non-serving base station 1106.

At step 1204, a coupled load indicator 1110 is received at the servingbase station 1104. In the exemplary embodiment, the coupled loadindicator 1110 is based on coupled load parameters measured at thenon-serving base station 1106 and represents a quality of the trafficchannel measured at the non-serving base station 1106 due to the reverselink transmissions 210 of the mobile station 1102 served by the servingbase station 1104.

At step 1206, the serving base station 1104 manages the reverse linktransmissions of the mobile station 1102 in accordance with the maximumtolerable coupled load 1112. In the exemplary embodiment, the servingbase station 1104 calculates the expected coupled loads of all mobilestations 1102 maintaining the non-serving base station 1106 in their setof active base stations. Using the coupled load indicator 1110 for eachmobile station 1102 and the mobile station transmission parameter ofeach mobile station 1102, the serving base station 1104 calculates theexpected coupled load for the mobile station 1102. The serving basestation 1104 schedules data transmission rates to the mobile stations1102 such that the total expected coupled load at the non-serving basestation 1106 will not exceed the maximum tolerable coupled load 1112during a future transmission. Accordingly, the serving base station 1104allocate resources to the mobile stations 1102 while conforming to thelimits provided by the non-serving base stations 1106 thereby minimizingthe likelihood of an overload condition at the non-serving base stations1106.

FIG. 13 is a flow chart of a method of managing reverse link channelresources at a base station 300 functioning as a non-serving basestation 1106 in accordance with the second exemplary embodiment of theinvention.

At step 1302, the base station 300 functioning as non-serving basestation 1106 to the mobile station 1102 forwards, to another basestation 300 functioning as a serving base station 1104 to the mobilestation 1102, a coupled load indicator 1110 based on coupled loadparameters measured at the non-serving base station 1106 due to reverselink transmissions of the mobile station 1102.

At step 1304, the non-serving base station 1106 determines the maximumtolerable coupled load. Various mobile stations rate requests arearranged in decreasing order of their priorities. After the mobilestations with higher priorities are assigned capacity, the mobilestations 1102 are assigned a capacity such that some fraction of maximumtolerable coupled load is equal to the capacity set aside for the mobilestations 1102.

At step 1306, a maximum tolerable coupled load 1112 representing themaximum allowable load is forwarded to the base station 300 functioningas the serving base station. In the second exemplary embodiment themaximum tolerable coupled load 1112 is transmitted through the backhaul208 to the serving base station 1104.

FIG. 14 is a flow chart of a method of allocating reverse link channelresources in a communication system 100 having geographicallydistributed base stations in accordance with the second exemplaryembodiment of the invention. As discussed above, the functions ofserving base stations 1104 and non-serving base stations 1106 may beperformed within a single base station 300 that functions as servingbase station 1104 to some mobile stations 110-114 and as a non-servingactive base station 1106 to other mobile stations 114.

At step 1402, all base stations that are maintained in an active list ofa mobile station 1102 that is served by another base station forward acoupled load indicator 1110 to the other base stations 1104 that areserving the mobile stations 1102. The coupled load indicators 1110 arebased on coupled load parameters measured at the base station 1106. Inthe second exemplary embodiment, the base station 1106 measures andforwards the Ecp/Nt values due to the reverse link transmissions ofmobile stations 1102 served by the other base stations 1104 and thatmaintain the base station 1106 in the set of active base stations.

A suitable notation for characterizing and describing relationshipsbetween the various base stations 300, 1104, 1106 includes usingsubscripts to denote a set of base stations. In the second exemplaryembodiment, each base station (BS j) that is in the active set of mobilestations (MSi), except where BS j∈ServingBS_MS_(i), measures andtransmits the (Ecp/Nt)ji to the serving base station for MSi. In thesecond exemplary embodiment, (Ecp/Nt)ji is used as a coupled loadindicator 1110. ServingBS_MSi is the set of serving base stations formobile stations (i) and(Ecp/Nt)ji(1+(T/P)(Ri)+(C/P))/(1+(Ecp/Nt)ji(1+(T/P)(Ri)+(C/P))) is thecoupled load experienced at the non-serving base stations (BSj) due tomobile stations (MSi) served by the serving base stations. (T/P)(Ri)refers to the traffic-to-pilot ratio of the traffic channel when thetransmission rate is Ri. (C/P) refers to the sum total of controlchannels (and fundamental channel) power to pilot power ratio. In theexemplary embodiment, a value representing the (Ecp/Nt)ji is transmittedto the serving base stations (BSk).

At step 1404, the base stations 300 functioning as serving base stations1104 receive coupled load indicators from base stations 1106 maintainedin the set of active base stations by mobile stations served by the basestations 1104.

At step 1406, the base stations determine a maximum tolerable coupledload 1112 due to mobile stations served by other base stations based onthe requests and priorities of mobile stations served by the basestations. A scheduler function in each base station j functioning as anon-serving base station reserves the maximum tolerable coupled loadcapacity 1112 (MaxTolerableCoupledLoad jk) for mobile stations served byother base stations.

At step 1408, the base stations forward the maximum tolerable coupledload to the other base stations. Accordingly, each base stationfunctioning as a non-serving base station forwards the maximum tolerablecoupled load capacity 1112 (MaxTolerableCoupledLoad jk) to the servingbase stations k.

At step 1410, base stations functioning as serving base stations receivethe maximum tolerable coupled loads 1102 from non-serving base stations1106 maintained in the set of active base stations of mobile stations1102 served by the base stations.

At step 1412, the base stations calculate the available capacity at thebase station for mobile stations served by the base stations functioningas a non-serving base station 1106 to some mobile stations and as aserving base station 1104 to other mobile stations. After reservingcapacity for all mobile stations 1102 served by other base stations,base stations functioning as the non-serving base-stations j calculatetheir available capacity according to the following equation:

${{Cav}_{j} = {{Cav}_{j} - {f \times {\sum\limits_{k}{MaxTolerableCoupledLoad}_{jk}}}}},$where Cav_(j) is the available capacity at the non-serving base stationj for scheduling the mobile stations for which the base station j is theserving base station. The factor f represents how conservative the basestation j is in reserving capacity for the mobile stations it is notresponsible for scheduling. f=0 represents the case where the basestation j doesn't reserve any capacity for the mobile stations it is notscheduling while f=1 represents the case where base station j is mostconservative.

At step 1414, the base stations manage reverse link transmissions byallocating reverse links resources in accordance with the maximumtolerable coupled loads 1112 received from other base stations. In thesecond exemplary embodiment, the base stations k allocate reverse linkresources by allocating transmission data rates to all mobile stations iserved by base stations k in accordance with the following criteria:

${\underset{:{j \in {{ActiveBS}{(i)}}}}{\sum\limits_{i:{k \in {{ServingBS}{(i)}}}}}{{CoupledLoad}_{jk}\text{(}R_{i}}},{{\left( {E_{cp}/N_{t}} \right)_{ij}\text{)}} < {{MaxTolerableCoupledLoad}_{jk}\frac{{Sin}\;{r_{ki}\left( {R_{i},\left( {C/P} \right)} \right)}}{1 + {{Sin}\;{r_{ki}\left( {R_{i},\left( {C/P} \right)} \right)}}}} \leq {Cav}_{k}}$

-   -   where CoupledLoad and Sin r are as defined above with reference        to the first exemplary embodiment.

Accordingly, each base station determines the coupled loads at the basestation due to mobile stations served by other base stations, reservescapacity for those mobile stations, forwards the maximum tolerablecoupled loads to all serving base stations serving those mobilestations, and allocates reverse link resources based on the availablecapacity for mobile stations the base station is serving and the maximumtolerable coupled loads received from non-serving base stations of themobile stations served by the base station.

FIG. 15 is a block diagram of a portion 1500 of a communication system100 providing communications services to mobile stations 110-114 withgeographically distributed base stations 102-108 in accordance with thethird exemplary embodiment of the invention. In most situations, thecommunication system 100 includes several base stations 1504, 1506 thatare strategically positioned to provide wireless communication servicesto numerous mobile stations 1502. Depending on the quality of thecommunication channels between a mobile station 1502 and the basestation (1504, 1506), the mobile station 1502 may be communicating withmore than one base station (1504, 1506) at any particular time. Asdiscussed above, each mobile station 1502 maintains a set of active basestations where the communication links between the mobile station 1502and the active base stations 1504, 1506 are adequate for communication.Of the active base stations, one base station performs as the servingbase station 1504 while the other base stations in the active set arenon-serving base stations 1506. Such situations typically occur during asoft handoff where a single base station performs the functions of aserving base station 1504 and one or more other base stations arenon-serving active base stations 1506. Where conditions warrant, therole of the serving base station 1504 is transferred to a base stationpreviously functioning as a non-serving active base station 1506 (i.e. ahandoff occurs).

In the interest of clarity, FIG. 15 includes blocks representing amobile station 1502 and two active base stations 1504, 1506 including aserving base station 1504 and non-serving base station 1506. Thoseskilled in the art will recognize, based on these teachings and knowntechniques, that a base station 300 may function as a serving basestation 1504 to numerous mobile stations 1502 and that any one mobilestation 1502 may maintain any number of active base stations 1504, 1506.The teachings discussed herein, therefore, may be extended to any numberof mobile stations 1502, serving base stations 1504, and non-servingbase stations 1506. As discussed below in further detail, the other basestations 300 may not have a communication link with the mobile station1502 of sufficient quality to become an active base station but maycontribute to the load experienced at any one of the active basestations 1504, 1506. The serving base station 1504 may be the first basestation 102, the second base station 104, or third base station 106discussed above with reference to FIGS. 1-4. The serving base station1504 may also function as a non-serving base station 1506 for anothermobile station (not shown in FIG. 15) and the non-serving base station1506 may function as a serving base station 1504 for other mobilestations (not shown in FIG. 15). Accordingly, a base station 102-108 maysimultaneously function as a serving base station 1504 to some mobilestations 1502 and as a non-serving base station to other mobilestations. The functions described herein for each of the base stations1504, 1506, therefore, are simultaneously performed by the other of thebase stations in most circumstances.

In the third exemplary embodiment, a base station 300 functioning as anon-serving base station 1506 estimates an expected coupled load 1508due to mobile stations 1502 served by other base stations 1504 andallocates reverse link resources in accordance with the expected coupledload 1508. Accordingly, no direct or explicit communication is sent overa backhaul 208 between the serving base station 1504 and the non-servingbase station 1506 in the third exemplary embodiment of the invention.The serving base station 1504 schedules all mobile stations 1502 it isserving based on the channel quality of the traffic channel received atthe serving base station 1504.

The non-serving base station 1506, schedules the mobile stations (notshown) served by the non-serving base station 1506 after making anestimate of the expected coupled load 1508 contributed by all the mobilestations 1502 it is not scheduling (i.e. serving) but that aretransmitting reverse link signals 210 that are received and processed bythe non-serving base station 1506. In some circumstances, theestimations of the expected coupled loads 1508 by the non-serving basestations 1506 are based on the measurements made of previoustransmissions of mobile stations 1502 in a soft-handoff with thenon-serving base station 1506. The estimation includes the totalexpected coupled loads from all mobile stations 1502 for which 1506 is anon-serving base station 1506 and that are served by any other basestation.

FIG. 16 is a flow chart of method, performed in a base station 300, ofmanaging reverse link resources in a communication system 100 havinggeographically distributed base stations in accordance with the thirdexemplary embodiment of the invention.

At step 1602, a non-serving base station 1506 measures at least onecoupled load parameter due to reverse link transmissions 210 of mobilestations 1502 served by other base stations 1504. In the third exemplaryembodiment, during every transmission interval, the non-serving basestation j measures the received pilot SNR ((Ecp/Nt)ji) and transmissionrate on control and voice channels contributed by all MS i that have BSj in the Active Set but are not scheduled by BS j. Based on (Ecp/Nt)jiand the transmission rate Ri, the total coupled load (TotCoupledLoadj)during the current transmission (indexed by n) are computed according tothe following equation:

${{TotCoupledLoad}_{j}\lbrack n\rbrack} = {\underset{j \in {{ActiveSet}{(i)}}}{\sum\limits_{i:{j \notin {{Serving}{(i)}}}}}\frac{{Sin}\;{r_{ji}\left( {R_{i},\left( {C/P} \right)} \right)}}{1 + {{Sin}\;{r_{ji}\left( {R_{i},\left( {C/P} \right)} \right)}}}}$where Sin r _(ji)(R _(i),(C/P))=(E _(cp) /N _(t))_(ji)(1+(T/P)(R_(i))+(C/P)).

At step 1604, the base station 1506 estimates the expected coupled loadfor a future transmission based on the measured total coupled load of atleast one previous transmission. Any of several techniques may be usedto estimate the expected coupled load for a future transmission(TotCoupledLoadj[n+1]) and the particular technique depends on the typeof communication system 100, the transmission structure of the reverselinks 210, 212 and other factors. One suitable technique includes usingthe measured TotCoupledLoadj[n] as the expected value forTotCoupledLoadj[n+1]. Another technique includes calculating a filteredaveraged value (Exp_TotCoupledLoadj) to estimate TotCoupledLoadj[n+1] asspecified by the following equation:

${{Exp\_ TotCoupledLoad}_{j}\left\lbrack {n + 1} \right\rbrack} = {\sum\limits_{i = 0}^{L}{\alpha_{i}{{TotCoupledLoad}_{j}\left\lbrack {n - i} \right\rbrack}}}$where α_(i) are the filter coefficients and L is the length of thefiltering. Signal processing schemes may be employed to estimate thecoefficients α_(i). Further, the coefficient α_(i) can be adaptivelychanged to minimize the mean square error between the estimatedTotCoupledLoadj[n+1] and the actual measured TotCoupledLoadj[n+1] attime instant n+1.

Therefore, a total coupled load due to reverse link transmissions 210 ofmobile stations served by other base stations for at least one previoustransmission is determined. The estimated expected coupled is based onthe previous total coupled loads and may be set equal to one of theprevious coupled loads or may be determined by processing a plurality ofcoupled loads for previous transmissions periods. Other techniques maybe used in some circumstances to determine the estimated expectedcoupled load based on previous coupled loads.

In systems with Hybrid-ARQ on reverse-link transmissions, thetransmission of a packet is performed by multiple transmissions untilthe packet is successively received. If the delay between the first andthe respective transmissions remain fixed, transmission line of a packetand its subsequent retransmissions is referred to as an ARQ instance.Due to retransmissions, a strong correlation between the coupled loadduring subsequent ARQ instances may exist. To take advantage of thiscorrelation, TotCoupledLoad may be estimated from previous transmissionsduring the same ARQ instance.

At step 1606, the base station manages reverse link transmissions 210 ofthe mobile stations served by the base station in accordance with theestimated expected coupled load 1508. In the third exemplary embodiment,the non-serving base-station j, after determining the estimated expectedcoupled load Est_TotCoupledLoadj[n+1], updates the available capacityfor scheduling the mobile stations that have base station j as theserving base station according to the following equation:Cav _(j) =Cav _(j) −Est_TotCoupledLoad_(j)

The base stations j allocate the reverse link resources such that thetotal available capacity is not exceeded in the third exemplaryembodiment. Accordingly, the base stations functioning as non-servingbase stations 1506, in the third exemplary embodiment, estimate anexpected coupled load due to all mobile stations 1502 served by otherbase stations 1504 and allocate reverse link resources to mobilestations served by the non-serving base station 1506 based on theremaining total capacity at the base station after taking into accountthe total expected coupled load.

Clearly, other embodiments and modifications of this invention willoccur readily to those of ordinary skill in the art in view of theseteachings. The above description is illustrative and not restrictive.This invention is to be limited only by the following claims, whichinclude all such embodiments and modifications when viewed inconjunction with the above specification and accompanying drawings. Thescope of the invention should, therefore, be determined not withreference to the above description, but instead should be determinedwith reference to the appended claims along with their full scope ofequivalents.

1. A method, performed in a base station functioning as a serving basestation to a mobile station, the method comprising: receiving, from theanother base station, a coupled load indicator of a coupled loadmeasured at the another base station, wherein the coupled load indicatorindicates a coupled reverse link load experienced at the another basestation and due to reverse link transmissions of the mobile stationbeing served by the serving base station and maintaining the anotherbase station in a set of active base stations; determining, based on thecoupled load indicator and a mobile station transmission parameter ofthe mobile station, an expected coupled load to the another base stationdue to the mobile station, wherein the another base station is anon-serving base station to the mobile station; and forwarding theexpected coupled load to be used by the another base station todetermine an available capacity for managing reverse link transmissions.2. A method in accordance with claim 1, wherein the forwarding theexpected coupled load comprises transmitting the expected coupled loadthrough a backhaul connected between the base station and the anotherbase station.
 3. A method in accordance with claim 1, wherein the mobilestation transmission parameter comprises a transmission data rate of areverse link transmission from the mobile station.
 4. A method inaccordance with claim 3, wherein the mobile station transmissionparameter comprises a transmission power level.
 5. A method inaccordance with claim 1, wherein the coupled load indicator representsan energy-per-chip-to-noise-plus-interference ratio (E_(cp)/N_(t))measured at the another base station.
 6. A method in accordance withclaim 1, wherein the expected coupled load represents an expectedenergy-per-chip-to-noise-plus-interference ratio (E_(cp)/N_(t)) at theanother base station.
 7. A method, performed at a base station, formanaging reverse link communication in a distributed base stationcommunication system, the method comprising: forwarding a coupled loadindicator to another base station, wherein the coupled load indicatorindicates a coupled load due to reverse link transmissions of a mobilestation being served by the another base station; receiving an expectedcoupled load from the another base station in response to the coupledload indicator, wherein the expected coupled load is an expected coupledreverse link load experienced at the base station due to reverse linktransmissions of the mobile station being served by the another basestation; determining an available capacity for the base station based onthe expected coupled load; and managing reverse link transmissions, inaccordance with the available capacity, among other mobile stationsidentifying the base station as a serving base station of the othermobile stations, wherein the base station is a non-serving base stationto the mobile station.
 8. A method in accordance with claim 7, whereinthe expected coupled load is based on a measured coupled load at thebase station and a mobile station transmission parameter of the mobilestation.
 9. A method in accordance with claim 8, wherein the mobilestation transmission parameter comprises a transmission rate of themobile station.
 10. A method in accordance with claim 8, wherein themobile station transmission parameter comprises a transmission powerlevel of the mobile station.
 11. A method in accordance with claim 7,wherein the determining the available capacity comprises: calculatingthe difference between the total capacity of the base station and atleast the expected coupled load.
 12. A method in accordance with claim11, wherein the calculating the difference comprises: calculating atotal load by summing the loads due to other sources and a plurality ofexpected coupled loads corresponding to a plurality of mobile stationsserved by a plurality of other base stations; and calculating thedifference between the total capacity and the total load to produce theavailable capacity.
 13. An apparatus as part of a base station in adistributed base station communication system, comprising: a controlinterface configured to receive, from another base station, a coupledload indicator of a coupled load parameter measured at the another basestation, wherein the coupled load indicator indicates a coupled reverselink load experienced at the another base station and due to reverselink transmissions of the mobile station being served by the basestation and maintaining the another base station in a set of active basestations; and a processor configured to determine, based on the coupledload indicator and a mobile station transmission parameter of the mobilestation, an expected coupled load to the another base station due to ananticipated transmission of the mobile station, wherein the controlinterface is configured to forward the expected coupled load to be usedby the another base station to determine an available capacity formanaging reverse link transmissions.
 14. An apparatus in accordance withclaim 13, wherein the control interface is further configured totransmit the expected coupled load through a backhaul connected the basestation and to the another base station.
 15. An apparatus in accordancewith claim 13, wherein the mobile station transmission parametercomprises a transmission data rate of a reverse link transmission fromthe mobile station.
 16. An apparatus in accordance with claim 15,wherein the mobile station transmission parameter further comprises atransmission power level.
 17. An apparatus in accordance with claim 13,wherein the coupled load indicator represents anenergy-per-chip-to-noise-plus-interference ratio (E_(cp)/N_(t)) measuredat the another base station.
 18. An apparatus in accordance with claim13, wherein the expected coupled load represents an expectedenergy-per-chip-to-noise-plus-interference ratio (E_(cp)/N_(t)) at theanother base station.
 19. An apparatus as part of a base station in adistributed base station communication system, comprising: a processorconfigured to: forward a coupled load indicator to another base station,wherein the coupled load indicator indicates a coupled load due toreverse link transmissions of the mobile station being served by theanother base station; receive an expected coupled load from the anotherbase station in response to the coupled load indicator, wherein theexpected coupled load is an expected coupled reverse link loadexperienced at the base station due to reverse link transmissions of themobile station being served by the another base station; determine anavailable capacity for the base station based on the expected coupledload; and manage reverse link transmissions, in accordance with theavailable capacity, among other mobile stations identifying the basestation as a serving base station of the other mobile stations, whereinthe base station is a non-serving base station to the mobile station.20. An apparatus in accordance with claim 19, wherein the expectedcoupled load is based on a measured coupled load parameter at the basestation and a transmission parameter of the mobile station.
 21. Anapparatus in accordance with claim 20, wherein the transmissionparameter comprises a transmission rate of the mobile station.
 22. Anapparatus in accordance with claim 20, wherein the transmissionparameter comprises a transmission power level of the mobile station.23. An apparatus in accordance with claim 19, wherein the processor isfurther configured to determine the available capacity by calculatingthe difference between the total capacity of the base station and atleast the expected coupled load.
 24. An apparatus in accordance withclaim 23, wherein the processor is further configured to calculate thedifference by: calculating a total load by summing the loads due toother sources and a plurality of expected coupled loads corresponding toa plurality of mobile stations served by a plurality of other basestations; and calculating a difference between the total capacity andthe total load to produce the available capacity.
 25. A non-transitorycomputer-readable medium storing instructions therein executable at abase station, the instructions comprising: instructions to receive, fromthe another base station, a coupled load indicator of a coupled loadparameter measured at the another base station, wherein the coupled loadindicator indicates a coupled reverse link load experienced at theanother base station and due to reverse link transmissions of the mobilestation being served by the serving base station and maintaining theanother base station in a set of active base stations; instructions todetermine, based on the coupled load indicator and a mobile stationtransmission parameter of the mobile station, an expected coupled loadto the another base station due to an anticipated transmission of themobile station, wherein the another base station is a non-serving basestation to the mobile station; and instructions to forward the expectedcoupled load to be used by the another base station to determine anavailable capacity for managing reverse link transmissions.
 26. Anon-transitory computer-readable medium storing instructions thereinexecutable at a base station, the instructions comprising: instructionsto forward a coupled load indicator to another base station, wherein thecoupled load indicator indicates a coupled load due to reverse linktransmissions of a mobile station being served by the another basestation; instructions to receive an expected coupled load from theanother base station in response to the coupled load indicator, whereinthe expected coupled load is an expected coupled reverse link loadexperienced at the base station due to reverse link transmissions of themobile station being served by the another base station; instructions todetermine an available capacity for the base station based on anexpected coupled load; and instructions to manage reverse linktransmissions, in accordance with the available capacity, among othermobile stations identifying the base station as a serving base stationof the other mobile stations, wherein the base station is a non-servingbase station to the at least one mobile station.
 27. An apparatus in abase station for wireless communications, the apparatus comprising:means for receiving, from another base station, a coupled load indicatorof a coupled load measured parameter at the another base station,wherein the coupled load indicator indicates a coupled reverse link loadexperienced at the another base station and due to reverse linktransmissions of the mobile station being served by the serving basestation and maintaining the another base station in a set of active basestations; means for determining, based on the coupled load indicator anda mobile station transmission parameter of the mobile station, anexpected coupled load to the another base station due to the mobilestation, wherein the another base station is a non-serving base stationto the mobile station; and means for forwarding the expected coupledload to be used by the another base station to determine an availablecapacity for managing reverse link transmissions.
 28. An apparatus inaccordance with claim 27, wherein the means for receiving is furtherconfigured to transmit the expected coupled load through a backhaulconnected the base station and to the another base station.
 29. Anapparatus in accordance with claim 27, wherein the mobile stationtransmission parameter comprises a transmission data rate of a reverselink transmission from the mobile station.
 30. An apparatus inaccordance with claim 29, wherein the mobile station transmissionparameter further comprises a transmission power level.
 31. An apparatusin accordance with claim 27, wherein the coupled load indicatorrepresents an energy-per-chip-to-noise-plus-interference ratio(E_(cp)/N_(t)) measured at the another base station.
 32. An apparatus inaccordance with claim 27, wherein the expected coupled load representsan expected energy-per-chip-to-noise-plus-interference ratio(E_(cp)/N_(t)) at the another base station.
 33. An apparatus in a basestation for wireless communications, the apparatus comprising: means forforwarding a coupled load indicator to another base station, wherein thecoupled load indicator indicates a coupled load due to reverse linktransmissions of a mobile station being served by the another basestation; means for receiving an expected coupled load from the anotherbase station in response to the coupled load indicator, wherein theexpected coupled load is an expected coupled reverse link loadexperienced at the base station due to reverse link transmissions of themobile station being served by the another base station; means fordetermining an available capacity for the base station based on theexpected coupled load; and means for managing reverse linktransmissions, in accordance with the available capacity, among othermobile stations identifying the base station as a serving base stationof the other mobile stations, wherein the base station is a non-servingbase station to the mobile station.
 34. An apparatus in accordance withclaim 33, wherein the expected coupled load is based on a measuredcoupled load parameter at the base station and a transmission parameterof the mobile station.
 35. An apparatus in accordance with claim 34,wherein the transmission parameter comprises a transmission rate of themobile station.
 36. An apparatus in accordance with claim 34, whereinthe transmission parameter comprises a transmission power level of themobile station.
 37. An apparatus in accordance with claim 33, furthercomprising means for determining the available capacity by calculatingthe difference between the total capacity of the base station and atleast the expected coupled load.
 38. An apparatus in accordance withclaim 37, further comprising means for calculating the difference by:calculating a total load by summing the loads due to other sources and aplurality of expected coupled loads corresponding to a plurality ofmobile stations served by a plurality of other base stations; andcalculating a difference between the total capacity and the total loadto produce the available capacity.
 39. A base station, comprising: areceiver; a control interface capable of receiving via the receiver,from another base station, a coupled load indicator of a coupled loadparameter measured at the another base station, wherein the coupled loadindicator indicates a coupled reverse link load experienced at theanother base station and due to reverse link transmissions of the mobilestation being served by the base station and maintaining the anotherbase station in a set of active base stations; and a processor capableof determining, based on the coupled load indicator and a mobile stationtransmission parameter of the mobile station, an expected coupled loadto the another base station due to an anticipated transmission of themobile station, wherein the control interface is capable of forwardingthe expected coupled load to be used by the another base station todetermine an available capacity for managing reverse link transmissions.40. A base station, comprising: a receiver; and a processor configuredto: forward a coupled load indicator to another base station, whereinthe coupled load indicator indicates a coupled load due to reverse linktransmissions of the mobile station being served by the another basestation; receive an expected coupled load from the another base stationin response to the coupled load indicator, wherein the expected coupledload is an expected coupled reverse link load experienced at the basestation due to reverse link transmissions of the mobile station beingserved by the another base station; determine an available capacity forthe base station based on the expected coupled load, received via thereceiver; and manage reverse link transmissions, in accordance with theavailable capacity, among other mobile stations identifying the basestation as a serving base station of the other mobile stations, whereinthe base station is a non-serving base station to the mobile station.